I'm in the process of getting my high school car back on the road.
440 9.6 to 1 TRW
Mopar performance .528 solid cam
Ported 906 heads with 2.14-1.81 crane gold roller rockers
Hooker headers
Offenhauser intake with holley 600 1850 vacuum secondary carbs. Progressive linkage.
4spd with 4.10

And now the question:
When I rebuild the carbs is there any advantage to leaving or eliminating the power valve in the secondary carb? Also any other tips/advice appreciated

Just finished tuning a customers 440 with an Air fuel ratio sensor and boy was that nice. I'm excited to get this old 440 running better than ever.

I'll give you my limited experience with dual carbs. I would keep both carbs the same and use a wide band to bring them in. When you introduce a variable in one carb, but not the other, now you can have issues getting the jetting under load correct. I don't see any advantage to removing the PV but YMMV. Go online to Diamondback Racing, they have the best tips I found on setting up dual quads. www.diamondbackengines.com Look under white pages-dual quads

The linkage is a bit of a question. I had better results with my 383 (OEM Chrysler 343 HP divided single plane iron manifold) with 2 AVS idling on both,
It's a trade-off: simultaneous has better distribution but more sensitive to vacuum changes.

Thanks for the responses. I read the Diamondback Racing dual quad article.

When I first got the engine running in '98 the carb linkage was 1 to 1. Car always seemed to run strong. 3700lbs 13.07 110mph on slippery Radial T/A tires. With modest tuning skills as a 20 year old I have to believe there is more on the table. This new wide band air/fuel gauge is a blessing.

At some point after that I built progressive linkage that worked well. Much nicer to drive around town. 15 or so years ago I installed adjustable jet plates in the secondaries - definite improvement. I just KNOW the jetting cant be optimal. Mostly I'm curious if there is anything else I should pay attention to. This is the only multi carb engine I've ever worked on.

The transition slot restriction will determine how smooth the power comes in from idle to mid range power. I don't like the idea of the progressive linkage. The vacuum secondaries are already acting as a progressive linkage. You are really screwing with the airflow and fuel distribution by having everything open at different times.

I was thinking the same thing as you guys making them tandem. He said he worked it though and it was a better all around situation with the progressive. I would just use the wide band and the a$$ometer to make everything happy? If tuning at the track, jet up until it slows down the go back a step.

I can’t think of any reason you wouldn’t want to retain the PV in both carbs running 1-to-1 linkage.

Removing it from “secondary” carb with a staged linkage might produce satisfactory results, depending on how far into the primary carb you are before the secondary kicks in.

Even with stock Holley 4150 carbs....... some utilize a secondary PV....... some don’t.

I would let the a/f gauge be your guide.


Fundamentally, it’s not any different than a street hemi with the factory staged linkage and a pair of AFB’s.

With dual Holley style vacuum secondary carbs, I’d connect both vacuum pods together so they worked in tandem.

How do you get an A:F reading on a specific vacuum point, w/o a dyno?

Find a long straight uphill section of road. A long mountain pass works but might not exist locally for most people.

Maybe consider Holley EFI sniper system instead...it is designed for tuning dual quads!


My 2 cents...

That really needs to be done with vacuum secondary carbs to get them both to open the same together you should make sure they both have the same springs in the vacuum pods also
The main thing I keep in mind on any inline dual quad motor with a single plane intake manifolds is to not starve the front cylinders by using progressive linkage
You do want instant throttle response, correct
On my pump gas street motors I've found they run really good and clean with 14.8 or higher AFR on the wide ban at light part throttle cruising below 2300 RPM

I wrote to Bill Jenkins in 1970 about jetting changes vs. linkage (383, 343 hp 2 X 4 factory manifold). I said "won't the vacuum at every opposing pair of ports change when progressive linkage moves?"
He agreed, no way to really fix it except testing.

Should the accelerator pumps be adjusted equally?

Absolutely
Do you know the way Holley recommends to adjust them? If not learn it now
What I remember about is and now do on mine is to hold the throttle wide open and push on the accelerator pump screw to see if it is bottomed out or not and if not bottom adjust the length so it has between .015 and .025 travel left between the accelerator arm and the screw at WOT
If it is bottom out adjust for between .015 and .025 travel left at WOT, this insures you won't rupture the pump by stepping hard on the throttle and you get maximum squirter volume

Thank you!